Patrick McConlogue, 23, said he passed by Leo Grand, 37, every day for five months. One day (Aug. 22, 2013, to be exact), McConlogue stopped and made the homeless man an offer: Grand could either have $100 to spend however he wanted or learn how to code from McConlogue.

"I went with door No. 2," Grand says on the video. McConlogue gave Grand three books on coding, and the two men met frequently to go over the lessons. Fast forward a few months, and McConlogue had taught Grand how to code and Grand created a mobile app that's now for sale.

The carpooling app for iOS and Android launched on Dec. 9 for 99 cents. It has already racked up a ton of positive publicity and user reviews. And it was built in just 109 days.

So, what exactly does the app do? Users can sign in and tell the app if they need a ride or want to give a ride. The app connects rider and driver. The end goal is to reduce the number of cars on the road and the pollution they produce and help people save money.

In the video, McConlogue says the process of bringing an app into the world has been extremely difficult and full of challenges he didn't anticipate. "But it is by far the most rewarding experience of my life," he says. "There are a lot of people who can do a lot of great things. And I think sometimes that potential can be lost."

Business Insider reports that all of the money the developers receive from the app will go toward Grand's programming education. McConlogue is reportedly working with other volunteers who have expressed an interest in teaching people how to code.